Actress engaged in long-term sexual relationship with dad of the Mamas and the Papas

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John Phillips poses for a photograph December 1, 1980 with his daughter MacKenzie while in drug rehab at Fair Oaks Hospital in Summit, New Jersey.

Updated at 4:33 PM EDT on Wednesday, Sep 23, 2009

Former child star Mackenzie Phillips revealed in her shocking new memoir that she engaged in an incestual relationship with her father, Mamas and the Papas musical group founder John Phillips -- and that the two slept together on the eve of her wedding.

Phillips, 49, who starred in TV sitcom "One Day at a Time" as a child, said in her tell-all book set to be released Wednesday that she and her father engaged in a relationship that she says started on the night before her wedding to Jeff Sessler, who toured with the Rolling Stones.

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"I woke up that night from a blackout to find myself having sex with my own father," she wrote. "Had this happened before? I didn't know. All I can say is it was the first time I was aware of it. For a moment I was in my body, in that horrible truth, and then I slid back into a blackout."

Phillips then began touring with her father in a band called the New Mamas and the Papas -- and during their time together, the sexual relationship became consentual.

Phillips also revealed that her father asked her to move to a place where their incest would be accepted or even welcomed.

"One night Dad said, 'We could just run away to a country where no one would look down on us. There are countries where this is an accepted practice. Maybe Fiji,'" Phillips wrote her father said.

Phillips, who was fired from "One Day at a Time" in 1980 for her constant drug use and went to rehab with her father the same year, said she felt from the beginning the incestual relationship was wrong.

"I thought, we're going to hell for this," she wrote.

Phillips also said this week that her father was the one who introduced her to cocaine.

"I remember going into my room, I was crouched on the floor...He put the needle in my arm and put the plunger in and he missed," said Phillips, who starred in "One Day at a Time" as a child actor.

"He missed the vein and my whole arm went numb," Phillips revealed.

Phillips, who pleaded guilty in 2008 to one count of felony cocaine possession and entered a year and a half-long drug rehab program post-arrest, said she began her drug habit hobnobbing with groupies and fellow musicians friends with her dad's group, the Mamas and the Papas.

Phillips' half-sister, Chynna Phillips, said Mackenzie told her of the incestuous affair in 1997, and said she believes it is true. She also confirmed that their father did drugs with Mackenzie.